Hi techxie007,
Well, this is a problem with opensource stuff. Initially developers get together and crunch out code in early stages. But as life moves on, so do their ambitions. I'm not complaining, but this is reality.
The developers who contributed to Rainbow had done a good job, but they have their full time jobs and life to take care of, too.
In short , don't expect a design document or architecture overview. I would be happy to look at one, if you find it or create one on your own.